For instance, a binocular (a stabiscope or the like) or a camera has a vibration-proof function. A prism of the binocular is driven and controlled by a direct motor; and an imaging element, or the like, of the camera is driven and controlled. Even in a situation where vibrations or hand movements arise, a stable state where vibrations are absorbed can be achieved. A pulse-width-modulation (PWM)-controlled circuit has hitherto been used as a drive circuit for such a motor.
FIG. 5 shows a configuration of a PWM-controlled motor drive circuit. As shown in FIG. 5, in the drive circuit, a Schottky diode 2 is connected in parallel to a driving motor 1 interposed between a source terminal Va and a ground, and a switching element 3, assuming the form of a field-effect transistor (FET) or the like, is connected in series with the driving motor 1. A PWM wave control circuit 4 is provided at a gate of the switching element 3. The PWM wave control circuit 4 generates a PWM wave having a frequency of, e.g., 54 KHz, in response to an input rotational frequency control signal, and sends the PWM wave to the switching element 3. By means of such a drive circuit, the switching element 3 performs switching operation at high speed and at a frequency of 54 KHz, and the rotation of the motor can be controlled by the drive power responsive to the pulse width.
By means of this PWM drive control operation, inductance existing in a coil of an armature of the motor 1 is effectively used. When the source current is not supplied, the stored power is supplied to the motor 1, so that high-speed switching operation is performed. Accordingly, a power loss, which would otherwise arise in an active range of a switching element—which is a drive transistor—another electronic element, is also diminished. Hence, an attempt can be made to achieve power savings.
However, the binocular, the camera, or the like employs a battery cell as the power source of a motor. Hence, PWM control is not enough to achieve sufficient driving efficiency, which raises a problem of the short life of the battery cell.
The function of the vibration-proof mechanism, or the like, of the binocular, the camera, and so on, entails performance of highly-responsive quick operation. Therefore, driving of the motor at a high rotational frequency is desired.